1. Field of the Invention
The present invention concerns a disposable apparatus for use in blood testing.
2. Description of Background Art
When making blood tests in the field, it is a desire to perform such tests with simple but reliable apparatus that can be handled even by relatively untrained personnel. Still, there exists the requirement that a blood sample shall be taken and handled under strict hygienic conditions, and that neither the sample itself or residues thereof, nor diluting or flushing liquids used when testing the sample shall risk to be contacted by humans. Thus, there shall be no waste matter and all contaminated material shall remain within the apparatus.
It is known in the state of art to count blood cells by causing a volume of diluted blood sample to pass a so-called capillary, i.e., an extremely small hole, generally in a ruby, the hole having a diameter considerably larger than the size of a blood cell, typically 80 μm. A voltage is applied over the capillary, and, when a blood cell passes through the hole, the electrical resistance changes. This is because the cells can be regarded as insulators. Each change in resistance can be detected by suitable electronic equipment, and the sum of all changes detected corresponds to the number of blood cells having passed through the capillary. In order to obtain the concentration of cells in the original sample, the concentration of cells in the diluted sample is multiplied by the dilution factor, typically 1:40000 when counting of red blood cells (RBC) is concerned. It is obvious, that measuring of sample volumes and dilution liquid volumes must be performed in an accurate and repeatable way such that not only a correct degree of dilution can always be guaranteed but also a thorough and uniform mixing of the two volumes is ensured.
A disposable sampling device for an apparatus for counting particles contained in a liquid, such as blood cells in a blood sample, is known from WO 99/01742. This device is capable of making one diluting step.
A blood testing apparatus for performing dilution of a small defined volume of blood sample contained in a capillary tube is described in U.S. Pat. No. 6,284,548. The dilution involves a pre-dilution step and a final dilution step.
A device for diluting and mixing a liquid sample, such as a blood sample for performing a CRP test, is described in WO 01/75416. The sample is contained in a capillary tube and is mixed in a first step with a diluting agent to provide a diluted sample. In a second step, a third medium, such as antibodies, may be mixed with the diluted sample.
Even if some of the prior art devices are capable of making two dilutions, none of them is capable of making two simultaneous dilutions to different dilution ratios, which is desirable in order to perform, e.g., simultaneous counting of white and red blood cells.